The present invention is directed to bicycles and, more particularly, to a shift control apparatus with preferential shifting of one of a front or rear transmission.
Some bicycles are equipped with shift control devices that automatically control the operation of front and rear transmissions (e.g., front and rear derailleurs that respectively cooperate with a plurality of front and rear sprockets) depending on bicycle velocity. An example of such a system is disclosed in JP 8-501,742. In that system, the bicycle chain may be engaged automatically with any combination of front and rear sprockets depending upon the velocity of the bicycle. The use of all sprocket combinations better accommodates more sensitive changes in riding conditions than is possible by operating the rear transmission alone and also avoids unnecessary shifting.
While conventional automatic bicycle transmissions use all sprocket combinations to accommodate many riding conditions and to avoid unnecessary shifting, sometimes large changes in gear ratio occur, thus imposing an undesirable burden on the rider's legs. To avoid this problem, it has been proposed to give preference to sequential shifting of the rear transmission. However, such operation can result in frequent and rapid successive shifting of the rear transmission under conditions of rapid acceleration or deceleration of the bicycle. Not only does multiple shifting of the rear transmission increase the overall time to achieve the desired gear ratio, it can also cause chattering of the rear transmission and undesirable multiple shocks to the rider's legs.